The existence of molecular sieves of the crystalline aluminosilicate type are well known to the art with numerous species having been found, both as naturally occurring materials and as synthetically formed materials. Numerous instances of the existence of these materials may be found in the art relating thereto and such will not be discussed herein.
The existence of crystalline microporous compositions which are other than zeolites, i.e., other than aluminosilicates, have been reported heretofore. For example, U.S. Pat. No. 4,310,440 discloses a novel family of crystalline, microporous crystalline aluminophosphate compositions.
Further, numerous patents have been obtained in compositions wherein metal and non-metal oxides have been deposited on an aluminosilicate. For example, U.S. Pat. No. 4,358,397 discloses a modified zeolite (aluminosilicate) which has been modified to have at least 0.25 weight percent of one or more Group IV A metals incorporated into the zeolite in the oxide form and at least 0.25 weight percent of phosphorus incorporated into the zeolite in the oxide form of phosphorus. The term "incorporation" is clarified in column 2, beginning at line 8 as being a " . . . treatment with a compound derived from one or more elements of Group IV A of the Periodic Table of Elements (i.e., Ti, Zr and Hf) to yield a composite containing a minor proportion of an oxide of such element." Similarly, the zeolites are disclosed as being treated with a phosphorus-containing compound to deposit a minor proportion of an oxide of phosphorus.
Although there has been an extensive treatment in the patent art and in the published literature of aluminosilicates and recently, aluminophosphates, there has been little information available on the presence of other than such materials. This is particularly true in the area of titanium containing compositions wherein titanium is present in the framework of the molecular sieve or so intimately related as to change the physical and/or chemical characeteristics of the molecular sieve. This is understandable in the question of aluminosilicates, as indicated by the article, "Can Ti.sup.4+ replace Si.sup.4+ in silicates?", Mineralogical Magazine, September vol 37, No. 287, pages 366-369 (1969). In this article it is concluded that substitution of framework silicon by titanium does not usually occur in aluminosilicates owing to the preference of titanium to be octahedrally bound rather than tetrahedrally bound. The formation of crystalline "titanosilicate zeolites*" is disclosed in U.S. Pat. No. 3,329,481, wherein a metallo-silicate complex is formed and treated to give the titano silicate product. The evidence for the claimed titanosilicate is based on the X-ray powder diffraction pattern data. The X-ray data are somewhat suspect as to whether such show substitution of titanium into the silicate framework inasmuch as the claimed X-ray patterns are also observed for the zirconium silicates and by the fact that similar X-ray patterns showing similar interplanar distances for the two values in patterns (B) have been reported for silicalite. (see GB No. 2,071,071 A). FNT *Obviously, the product is not a zeolite since it is not an aluminosilicate.
The incorporation of titanium in a silicalite type structure is disclosed in GB No. 2,071,071 A, published Dec. 21, 1979. The amount of titanium claimed to be substituted into the silicate-type structure is very small, being no more than 0.04 mole percent, based on the number of moles of silica, and may be as low as 0.0005. The titanium content was determined by chemical analysis and was not determined to be greater than 0.023 in any case. As indicated by a comparison of FIG. 1a and FIG. 1b, the amount of titanium present is small and no significant change in the X-ray diffraction pattern of silicalite was observed and the minor changes observed may simply be due to occluded titanium dioxide. Thus, absent other analytical data the results are not well defined. No comparison data for titanium dioxide are disclosed.
In view of the above, it is clear that the substitution of titanium into a zeolitic-type framework is conceived to be possible, wherein titanium substitutes for silicon, but difficult of proof. The substitution of titanium in non-zeolitic materials has not hereto been disclosed although a number of minerals have been found to contain titanium (see: "Can Ti Replace Si in Silicates", supra). Further, although titanium has been postulated to substitute for silicon in the aluminosilicate framework it has not heretofore been considered as to what occurs when silicon is not present. Specifically, these questions have not heretofore been considered in the art with respect to titanium substitution in aluminophosphate molecular sieves and such is the subject of the instant invention.